Long Term Evolution (LTE), a radio access technology standardized by the 3rd Generation Partnership Project (3GPP), is based on orthogonal frequency division multiplexing (OFDM) in the downlink and single-carrier frequency domain multiple access (SC-FDMA) in the uplink. This use of OFDM and SC-FDMA divides transmission resources into time resources and frequency resources. Time resources are divided into subframes that are each 1 ms in duration. Each subframe is in turn generally divided into 12 or 14 slots, each of which is occupied by one OFDM or SC-FDMA symbol. Frequency resources in each subframe are divided into subcarriers. The combination of a particular slot at a particular subcarrier is referred to as a resource element (RE). The subframe can thus divide transmission resources into a plurality of REs. The REs can be organized into resource element groups (REGs) and physical resource blocks (PRBs). Each REG includes, for example, 4 consecutive REs, while a PRB includes, for example, 72 REs (6 slots×12 subcarriers) or 84 REs (7 slots×12 subcarriers).
The subframe may also be divided into a control region and a data region. The control region may include, for example, 3 slots that carry physical downlink control channels (PDCCHs). The PDCCHs are used to carry downlink control information (DCI) messages. Each PDCCH may be allocated transmission resources in units of control channel elements (CCEs). Each CCE includes, for example, 9 consecutive REGs. An aggregation level (L) indicates how many contiguous CCEs (also referred to as consecutive CCEs) are allocated to a PDCCH. Example aggregation levels include 1, 2, 4, 8. An aggregation level of 2, for example, indicates that a PDCCH is allocated 2 consecutive CCEs.
Each PDCCH generally carries 1 DCI message. The DCI message may indicate, to a particular subframe recipient, which PRBs in the data region are intended for that recipient. For instance, a base station (e.g., evolved node B (eNB)) may include data for different wireless communication devices (WCDs) in one subframe. The base station may include, for each of those WCDs, a DCI message that indicates which PRBs in that subframe are intended for that WCD.
Different DCI formats exist for packing formatting information into a DCI message. Example formats include DCI formats 0, 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3, 3A, and 4. DCI formats 0, 3, 3A, and 4 are used for granting uplink (UL) transmission resources to WCDs. DCI formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, and 2C are used for assigning downlink (DL) resources to WCDs (see 3GPP 36.212, section 5.3.3). Different formats may provide for different DCI message sizes. That is, each DCI format may be associated with a certain DCI message size. A DCI message with a DCI format of 2 may, in one example, have a larger size than a DCI message with a DCI format of 1, though DCI message sizes may depend on a subframe's bandwidth. Some DCI formats may be associated with the same DCI message size. For example, a DCI message with a DCI format of 1A may have the same size as a DCI message with a DCI format of 0, 3, or 3A.
Some DCI formats may support a spatial multiplexing scheme that uses multiple input/multiple output (MIMO) techniques to transmit different layers (e.g., streams) of data on different transmitters toward different receivers. For instance, a base station may use a transmission rank of 2 to transmit two different streams of data on two respective antennas toward two receivers of a WCD. In some instances, the base station may limit transmission rank to 1, in which case, as an example, it transmits a single stream of data on one or more transmitters.
During handover (HO) of a wireless communication device (WCD) (e.g., a user equipment (UE)) there may be messages that are sent to/from the WCD while the WCD is in a problematic radio environment (e.g., when the WCD is at the cell edge). This can then lead to disruption of the connection or longer interruption times.
To obtain scheduling flexibility, and to use MIMO and the discontinuous allocation properties of OFDM, DCI format 2A is normally used for transmitting downlink (DL) messages. However, there is an imbalance for PDCCH Format 2A for DL and PDCCH Format 1A for UL of up to 1.7 dB for 20 MHz bandwidth since the used DL format is larger than the UL format.
Therefore, the base station can receive UL PDCCH grants while not receiving the DL assignments, which degrades voice quality. An example of this imbalance is where the base station can receive measurement reports but the WCD cannot hear the handover command.